CHAPTER IV. 

 THE SOIL. 



While, as we have seen, plants get by far the larger part of their structure 

 from the air, they get by far the most important matters from the soil, so far 

 as the making of a crop is concerned. While the carbon-di-oxide in the air 

 and the oxygen itself are essential to plant growth, the soil and the matters 

 which it furnishes are also essential. Some idea, therefore, of the origin of 

 soils and their nature and composition is essential to a proper understanding 

 of plant life, and the means for best sustaining and improving it. 



Back in the eighteenth century, the great French chemist, Lavoisier, 

 enunciated the great truth that in this earth nothing is created and nothing 

 is destroyed. That is, all substances that now exist have existed from the 

 beginning and will always exist. We cannot create anything ; we can simply 

 make new combinations of things already existing in soil and air, and when 

 this new combination is destroyed, these matters go back to the forms in 

 which they were acquired. We grow a tree from materials existing in soil 

 and air. Finally we burn the tree and get back the heat it originally got 

 from the sun. It is destroyed as a tree, but the carbon-di-oxide and water 

 and nitrogen have gone back where they came from, into the air; we have 

 left a handful of ashes, representing what it got from the soil, and these we 

 put back in the soil, where they can be used over again to build other plants. 

 The elements that went to make up the tree are still in existence, just as they 

 were before they were combined into a tree; and so in soil and air nature is 

 simply working over the same old materials and forming new combinations. 

 . The soils that form the foundation for our farms are all the result of the 

 gradual breaking down of the old earth-crust, and the crumbling and pulver- 

 izing of the rocks through natural agencies. When the earth first cooled 

 from a molten ball, the old, crystalline rocks were formed, and in the lapse 

 of ages other rocks were formed under water, and afterwards were elevated. 

 As soon as rocks are above the sea the process of disintegration begins. The 



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